• Protoctista/protozoa are single celled organisms.

• Most species are harmless.

• Many species are very useful and live in close association with other organisms in a mutualistic relationship (they work together to benefit each other).

• They range in length from 0.1 to 2mm and vary greatly in shape.

Protoctista / protists

seaweed is a protist

• Most fungi are saprophytes (they eat dead things).• Parasitic fungi can live within and on

human tissues and cause disease.• Trichophyton is a fungus which lives in the skin (a dermatophyte) and causes athlete’s foot• Characteristically it causes itching,

cracking and irritation on the feet, but can also affect the groin (“jock itch).• Another species of this fungus causes ringworm.

Fungi

Trichophyton (athlete’s foot) infection in the hand

Fungi reproduce asexually with spores

a. Nematodes (roundworms)Most live freely in water and soil.Many cause diseases and have rather spectacular effects on the body.

e.g. Loa Loa filariasis (African eye worm)Lives in tissues just beneath the skin of humans and baboons. At night they live in the lungs.Is carried by Deer flies and mango flies.Adult worms can live up to 17 years.

Invertebrates

Only a few flatworms cause diseases in humans.e.g. Taenia sp. (tapeworm)Infection occurs when raw or undercooked meat of an infected animal is eaten (beef or pork).Tapeworms can grow to 4m in length and can live for years.They usually do not cause any symptoms in the carrier.

Platyhelminthes (flatworms)

Tapeworm

Pulling a guinea worm out

A tapeworm inside a human

• Viruses are acellular (they do not have their own cells). • They consist only of a nucleus (RNA or DNA) inside a protective coat of protein.• Viruses are non-living but they can make

more of themselves by hijacking the cell machinery of host cells. They do not have an energy-producing system of their own.

Viruses

HIV

Virus Life Cycle

The flu is cause by one of a million variations of the virus.